At Pro events everyone uses telephoto
lenses (e.g. 70-200) because you get a stage to stand on and nobody is allowed in front of you. At more informal events it's a free for all and sometimes you have to go closer and use a general zoom otherwise people will stand in front of you and block your view
At modelling events, the photographer's ability plays only a minor part, you're at the mercy of the lighting guy basically.
At professional gigs, they set up the lighting very nicely so you can basically just point and shoot, e.g:
This shot goes into the trash because the model didn't look into my camera, but you can see the available
light is very nice, so you don't need flash at all IF (and it's a bit IF) the organisers and lighting people know what they are doing
Flash is only needed when the venue lighting is shocking (i.e. the lighting people don't know what they are doing)
I was at this one event where it was quite shockingly lit (there were floodlights along the bottom...the effect was like shining a torch at someone's face...). There was no way available
light was going to cut it and I had to use flash at this event and bounced it off a side
What available
light looked like was absolutely terrible...no amount of photoshop can fix this:
How I had to deal with it (bounce flash to 3 o'clock position):
If you want photos of EVERYONE, you will need at least 2 flashes and a battery pack otherwise your flash will overheat and auto shut down if you have to constantly fire it.